1. Field of the Invention
The present invention relates to a fuel-injection apparatus for an internal combustion engine.
2. Related Art
Conventionally, as illustrated in FIG. 12, the fuel injection apparatus having a control pressure chamber on opposite side of an injection port of a nozzle needle has been known, in which the start timing or the end timing of the fuel injection by the nozzle needle is controlled by adjusting pressure in the control pressure chamber (paper by IMH Co. at the Vienna Motor Symposium).
In FIG. 12, an injector 140 includes a nozzle needle 142 slidably disposed in an axial direction within a casing 141, and fuel which is supplied from a common rail (not illustrated) through a fuel passage 151 to a fuel chamber 146 is injected from an injection opening 147. A piston 144 is disposed reciprocatably with the nozzle needle 142 on an opposite side of the injection opening 147 of the nozzle needle 142. The nozzle needle 142 is urged by a compression coil spring 143 in a closing direction. A control pressure chamber 145 is defined by an end face of the piston 144 on an opposite side of the nozzle needle 142 and an inner wall of the casing 141. Fuel is supplied through the orifice 153 from the fuel passage 152 to the control pressure chamber 145. The control pressure chamber 145 is also connected to a pressure control valve 150 through an orifice 154. The pressure control valve 150 is a two-position and two-port solenoid valve. Leaked fuel within the casing 141 is discharged from a fuel passage 155 to a fuel tank (not illustrated.) When the pressure control valve 150 is closed as shown in FIG. 12, high-pressure fuel from the common rail is supplied to the control pressure chamber 145 without being discharged to the fuel tank 145. Thus, the nozzle needle 142 is closed by the sum of urging force of a compression coil spring 143 and pressure, exerted upon a pressure-receiving surface of the piston 144, of the control pressure chamber 145. Additionally, when the pressure control valve 150 is open, an amount of fuel discharged from the control pressure chamber 145 to the fuel tank through orifice 154 and pressure control valve 150 is greater than an amount of fuel discharged from the common rail to the control pressure chamber 145, because passage area of the orifice 153 is smaller than that of the orifice 154. Accordingly, when pressure within the control pressure chamber 145 declines, the nozzle needle 142 is lifted by the pressure of high-pressure fuel in the fuel chamber 146, and fuel is injected from the injection opening 147.
In the injector 140 illustrated in FIG. 12 high-pressure fuel keeps on being discharged to the fuel tank through the orifice 154, while the pressure control valve 150 is open. Therefore, an additional amount of fuel corresponding to the discharged amount must be supplied to the injector 140 in addition to the amount of injection fuel, and thereby the fuel supply pump for supplying fuel to the common rail becomes large in size and the efficiency of the fuel supply system is deteriorated. Moreover, when the pressure control valve 150 is closed, high-pressure fuel is supplied to the control pressure chamber 145 through the orifice 153 and pressure within the control pressure chamber 145 rises gradually. Therefore, there is a problem in that closing of the nozzle needle is delayed.
In order to solve the above problem of the delay in closing of the nozzle needle, the fuel injection apparatus illustrated in FIG. 13 has been proposed (paper by IMH Co. at the Vienna Motor Symposium). According to this apparatus, a communication between the fuel tank and the control pressure chamber 145 as well as a communication between the common rail and the control pressure chamber 145 are open and closed by a pressure control valve 161 which is a two-position and three-port solenoid valve. A check valve 163 for preventing fuel from flowing from the control pressure chamber 145 to the pressure control valve 161 and a pilot valve 162 having an orifice 164 are provided in a fuel passage. In FIG. 13, an injector 160 is in a closed state. When the pressure control valve moves from a position, where the pressure control valve communicates with the fuel tank, to the position illustrated in FIG. 13 after the fuel injection ends, high-pressure fuel from the common rail is rapidly supplied to the control pressure chamber 145 passing through check valve 163, thereby closing delay of the nozzle valve 142 being prevented.
Even in the fuel injection apparatus illustrated in FIG. 13, however, fuel is discharged from the control pressure chamber 145 to the fuel tank every time fuel is injected, therefore, it is necessary to supply, from the fuel supply pump to the common rail, several times as much fuel as the amount of injection fuel. For this reason, the fuel supply pump becomes large in size, and the diameter of fuel piping to supply fuel to the injector 160 also becomes large, thereby causing a problem in which efficiency of the fuel supply system being deteriorated. Moreover, there is a problem in that the cost is increased because the structure of the pressure control valve 161 is complicated.